The drinks industry is planning a ruthless campaign of economic incentives and psychological tricks to get customers to drink as much as possible when licensing laws are relaxed, The Observer can reveal.

Managers of massive 'vertical drinking' pubs are being offered bonuses worth up to £20,000 a year if they beat targets as the industry moves to exploit Britain's binge drinking culture.

Managers are so concerned about the consequences of the pressure to sell that they have laid bare a litany of tricks and sharp practices that will be used to maximise profits once 24-hour opening is legalised next month.

Managers for many of the big chain pubs dominating Britain's city centres are being ordered to draw up business development plans explaining how they will keep people in their pubs after 11pm and offered shares of the profits if they beat sales targets. One manager told of races between bar staff to sell as many 'shots' of spirits as possible within a set time and constant pressure to 'upsell' singles to doubles.

Dave Daley, head of the National Association of Licensed House Managers, which represents Britain's thousands of pub managers, broke cover this weekend to reveal the plans. He said he was speaking out as a warning to his members not to jeopardise their livelihoods and relations with neighbouring communities by giving in to the ferocious drive to profit from bingeing.

'I have been a manager for 30 years in these superpubs and in town centres,' he said. 'How we make our money is to make people binge drink: the more people drink, the more I get as a bonus. The more alcohol you sell, the more bonus you get: they give you a target to reach.

'We have these extra hours and companies are saying to managers "Give me your business plan, what are you going to do after 11 o'clock? If you sell x more we will give you more".'

Bonuses could be up to £20,000 a year, he said. Managers were being told that for the extra two hours they can open under the new laws, they could sell, for example, £2,000 worth of extra stock and keep 10 per cent of that as a bonus.

Daley's frank admissions will be taken seriously because they represent the first indication from within the industry - which has lobbied for the relaxation of the licensing laws - that the extensions are likely to have harmful consequences.

The industry was within its rights to make a profit, Daley said, but the big chains must recognise they could not treat alcohol like any other product: 'The difference between us and other selling operations is that we are selling a drug,' he said.

His comments come as an Observer investigation revealed the alarming ease with which customers can overindulge. A female reporter bought the equivalent of 64 units of alcohol in a Reading pub, ostensibly to share with a friend - enough alcohol to drink themselves to death - without once being challenged. The weekly recommended alcohol intake for a woman is 21 units.

The laws will be relaxed on 24 November when pubs that have successfully applied to vary their licences will be able to stay open longer. Ministers and the industry have insisted that it will not mean people simply drinking more, but a shift to a more relaxed, continental-style attitude, with people going out later in the evening.

James Purnell, the licensing minister, said irresponsible drinks promotions would be specifically targeted under the legislation and those found to be infringing it could lose their licences.

'Any chain using irresponsible drinking promotions to boost its profits isn't operating in the real world,' he said. 'Public opinion has hardened since the mid-1990s and the act does put people on notice that we expect to make irresponsible drinks promotions a thing of the past.'

Daley, however, said that opening later would inevitably have an impact: 'People are going to drink more, no doubt about it. Your sales are going to go up by 10-15 per cent. All this stuff about a cafe society is a lot of rubbish.'

Plans to keep drinkers in the pub after 11pm are likely to include curry nights, quiz nights or karaoke, he said, but there were concerns that pressure to maximise profits would lead to more noisy late-night entertainment which would badly affect neighbourhoods.

Mark Hastings of the British Beer and Pub Association, which represents the big managed pub chains as well as breweries, denied acting irresponsibly. Food was now a boom area for pubs and managers could meet sales targets by selling more of it, he suggested, even late at night.

'Just think of the number of people who go for a late-night curry,' he said. 'As for incentives related to sales, it would be totally misinterpreting them to say this is only related to selling drink. It's about "can you draw more customers to your pub, can you pull customers away from other pubs?" These are all ways of increasing profits.'

However, one former pub manager told The Observer that high-pressure sales tactics used in her pub were on orders from head office: 'Our job was to make as much money as possible - how could we do that except by selling as much alcohol as possible?'

Daley said pub managers worked on the assumption that after three or four drinks a customer was 'captured' and would stay: 'The profession is to get people half drunk and happy.'

The pressure to sell is now likely to be debated in the Commons tomorrow, when the Tories will call for a U-turn on relaxing the laws.

'Many are worried about the government allowing pubs to serve drink into the early hours of the morning, and reports that pressure is being put on bar staff to serve more and more alcohol to customers are a very real concern,' said Shadow Culture Secretary Theresa May.